1. Field of the Invention
This invention relates to a continuous process for annealing zirconium and zirconium alloys. More specifically, it deals with the use of a nitrogen atmosphere which allows the process to be continuous.
2. Description of the Prior Art
The idea of continuous annealing of metals is old in the art. Even the idea of continuous annealing in a nitrogen atmosphere has been used in annealing steel and certain metals. This shown in U.S. Pat. No. 4,183,773, Kawasoko et al, wherein a hydrogen-nitrogen atmosphere is used.
It has also been known to nitride metals including zirconium for the purpose of producing hardness. This hardness, however, is effected at the expense of ductility.
The usual way of annealing zirconium or zirconium alloys is by vacuum annealing since these metals are very reactive and considerably more reactive than steel. This vacuum annealing is extremely expensive not only with regard to equipment, but also with regard to operation. There is a need for a continuous process for annealing zirconium and zirconium alloys for economic purposes. However, a nitrogen atmosphere which would be an inexpensive atmosphere, has been avoided because of the reactivity of these metals. This is also recognized by MacEwen et al, U.S. Pat. No. 4,000,013, where a vacuum atmosphere is stated as preferred over helium or argon which have been treated to remove all traces of deleterious substances such as oxygen, nitrogen, etc.